Privileged planet: how CO^2 is a greenhouse gas (Introduction)

by David Turell , Thursday, August 08, 2024, 18:57 (108 days ago) @ David Turell

Quantum effects:

https://www.quantamagazine.org/physicists-pinpoint-the-quantum-origin-of-the-greenhouse...

"In 1896, the Swedish physicist Svante Arrhenius realized that carbon dioxide (CO2) traps heat in Earth’s atmosphere — the phenomenon now called the greenhouse effect. Since then, increasingly sophisticated modern climate models have verified Arrhenius’ central conclusion: that every time the CO2 concentration in the atmosphere doubles, Earth’s temperature will rise between 2 and 5 degrees Celsius.

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"First, in 2022, physicists settled a dispute over the origin of the “logarithmic scaling” of the greenhouse effect. That refers to the way Earth’s temperature increases the same amount in response to any doubling of CO2, no matter the raw numbers.

"Then, this spring, a team led by Robin Wordsworth of Harvard University figured out why the CO2 molecule is so good at trapping heat in the first place. The researchers identified a strange quirk of the molecule’s quantum structure that explains why it’s such a powerful greenhouse gas — and why pumping more carbon into the sky drives climate change.

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"...global warming is tied to a numerical coincidence involving two different ways that CO2 can wiggle.

“'If it weren’t for this accident,” Pierrehumbert said, “then a lot of things would be different.”

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"A key question was the origin of the logarithmic scaling of the greenhouse effect — the 2-to-5-degree temperature rise that models predict will happen for every doubling of CO2. One theory held that the scaling comes from how quickly the temperature drops with altitude. But in 2022, a team of researchers used a simple model to prove that the logarithmic scaling comes from the shape of carbon dioxide’s absorption “spectrum” — how its ability to absorb light varies with the light’s wavelength.

"This goes back to those wavelengths that are slightly longer or shorter than 15 microns. A critical detail is that carbon dioxide is worse — but not too much worse — at absorbing light with those wavelengths. The absorption falls off on either side of the peak at just the right rate to give rise to the logarithmic scaling.

“'The shape of that spectrum is essential,” said David Romps, a climate physicist at the University of California, Berkeley, who co-authored the 2022 paper. “If you change it, you don’t get the logarithmic scaling.”

The carbon spectrum’s shape is unusual — most gases absorb a much narrower range of wavelengths. “The question I had at the back of my mind was: Why does it have this shape?” Romps said. “But I couldn’t put my finger on it.” (my bold)

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"A photon of 15-micron light contains the exact energy required to set the carbon atom swirling about the center point in a sort of hula-hoop motion. Climate scientists have long blamed this hula-hoop state for the greenhouse effect, but — as Ångström anticipated — the effect requires too precise an amount of energy, Wordsworth and his team found. The hula-hoop state can’t explain the relatively slow decline in the absorption rate for photons further from 15 microns, so it can’t explain climate change by itself.

"The key, they found, is another type of motion, where the two oxygen atoms repeatedly bob toward and away from the carbon center, as if stretching and compressing a spring connecting them. This motion takes too much energy to be induced by Earth’s infrared photons on their own.

"But the authors found that the energy of the stretching motion is so close to double that of the hula-hoop motion that the two states of motion mix with one another. Special combinations of the two motions exist, requiring slightly more or less than the exact energy of the hula-hoop motion.

"This unique phenomenon is called Fermi resonance after the famous physicist Enrico Fermi, who derived it in a 1931 paper. But its connection to Earth’s climate was only made for the first time in a paper last year by Shine and his student, and the paper this spring is the first to fully lay it bare."

Comment: Note my bold. Is C0^2 so unusual a gas because it was designed to be different? Without global warming we wouldn't be here. This is another of Gould's 'contingencies' for life to occur.